This invention relates to a method for continuously manufacturing a synthetic resin tube and more particularly to a method for continuously manufacturing a synthetic resin tube from pre-molded flat strips of synthetic resin material in situ at a working site.
One of the commonly known methods for producing a synthetic resin tube comprises passing a synthetic resin material through a circular slit die of an extruder to thereby form tubular shape directly. In cases where a synthetic resin tube having a large diameter is produced, a large sized extruder is required. Moreover, when tubes having different diameters are produced, dies having corresponding diameters are required, resulting in high manufacturing costs.
Another method for producing a synthetic resin tube comprises forming a corrugated tube from a strip of synthetic resin in a softened state by the use of a plurality of rotating rollers arranged in a circular array such that the rollers define an imaginary cylinder about its central axis with the axes of the rollers being parallel to each other but angled relative to the central axis of the imaginary cylinder whereby as the rollers rotate the strip is helically wrapped around and advanced axially along the imaginary cylinder with portions of adjacent turns of the strip overlapping and joined together to form a continuous tube. In this method, however, only a single strip of synthetic resin material is wrapped around the imaginary cylinder with portions of adjacent turns of the strip overlapping one on another so that when the strip having a small thickness is employed, the width of the strip must be large in order to have wide overlapping portions, thus maintaining a certain tube wall thickness. This leads to considerable loss of manufacturing efficiency. On the contrary, when the strip having a large thickness is employed, it is quite difficult to have the tube all thickness uniform, while at the same time overlapping portious of the strip are raised to form stepped portions.
Alternatively, known synthetic resin tubes are produced in factories and transported by trucks and the like, which frequently necessitates high costs for transportation.